1. Field of the Invention
The present invention relates to an accessory for a linear transmission system, and more particularly to a lubrication device which is stored with lubricating grease.
2. Description of the Prior Art
A ball screw essentially comprises a nut, a screw shaft and plural balls capable of rolling between the nut and the screw shaft. With the balls, the nut and the screw shaft can slide relative to each other. The ball screw is widely applied onto various precise mobile machines due to its advantages of high smoothness and accuracy, such as various fine machining or semiconductor equipments. Therefore, lubrication to the helical groove is quite important. However, if the ball screw lacks lubrication for a long period, the friction between the nut and the screw shaft will be consequently increased, thus accelerating the abrasion of the ball screw.
In order to effectively reduce the abrasion of the ball screw caused by friction, lubrication systems for the conventional balls screws are divided into two types: the first type of lubrication system is stored with lubricating oil, disposed at both ends of the nut first, and is provided with an oil absorbent which is used to directly apply the lubricating oil onto the screw shaft to lubricate the helical groove thereof; the second type of lubrication system is provided with two oil-containing wipers which are disposed at both ends of the nut to lubricate the helical groove in the screw shaft by being in direct contact with the surface of the screw shaft.
The existing self-lubricating screw shafts are normally equipped with an external accessory which is filled with lubricant-soaked wool felt and fixed to the outside of the nut, so that when the screw shaft rotates relative to the nut, the wool felt will apply the lubricating oil into the helical groove of the screw shaft to lubricate the screw shaft. Since most of the semiconductor industries require a dust free environment, this lubrication method has to use the lubricating oil as lubricant, however, the lubricating oil is liquid and prone to producing particles which will adversely affect the cleanness of the environment, therefore, the existing designs are inapplicable to the semiconductor industries which require highly clean environment.
To solve the above problems, referring to FIG. 9, a lubrication system disclosed in U.S. Pat. No. 5,782,135 is provided with plural spacing balls 92 between rolling elements 91, and the spacing balls 92 are made of solid lubricating material (such as molybdenum disulfide, gold, silver, lead or PTFE), so that when the ball screw is in use, lubricating debris will be produced through abrasion of the spacing balls 92 against the rolling elements 91 to lubricate the rolling elements 91, the screw shaft and the nut. However, the above lubrication system also suffers from the following drawbacks in practice:
1. The spacing balls will lose the lubrication function after abrasion, and if the spacing balls are reduced to a certain scale through abrasion, stuck fault will be caused, interfering with the normal operation of the rolling elements.
2. Due to using the spacing balls to offer the lubrication function, the lubrication efficiency is unstable and difficult to control, causing insufficient lubrication which shortens the service life of screw shaft.
In addition, if lubricating grease replaces lubricating oil as lubricant, it can be used in a highly clean environment of the semiconductor industry, such as clean room, but the existing lubrication systems all need an external power source to push the lubricating grease into the interior of the ball screw (since the flowability of the lubricating grease is low, external power is needed), so that additional devices are needed to supply the power, thus occupying large space while increasing the equipment cost.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.